1. Field of the Invention
The present invention relates generally to a wafer surface machining apparatus, and more particularly to a wafer surface machining apparatus for grinding the reverse surface of a semiconductor wafer in a semiconductor wafer manufacturing process.
2. Description of Related Art
A surface machining apparatus for grinding the reverse surface of a semiconductor wafer generally comprises a housing stage for containing the wafers, a grinding stage for grinding the wafers, and a suction transfer device for transferring the wafers between the housing stage and the grinding stage. The conventional suction transfer device has a plurality of suction pads on a holding surface of a suction disc, and holds the wafers on the suction pads by suction.
Recently, there has been a desire for thin semiconductor wafers as ICs have become increasingly integrated. For this reason, the surface machining apparatus grinds the wafer thin.
The surface machining apparatus is provided with a chuck table, a grindstone, and a reverse surface cleaning device. The obverse surface of the semiconductor wafer is held on the chuck table and the grindstone is pressed against the reverse surface of the semiconductor wafer. The chuck table and the grindstone are rotated to grind the reverse surface of the wafer. On completion of the grinding, the wafer is removed from the chuck table, and then the reverse surface cleaning device cleans the reverse surface of the wafer.
An example of the reverse surface cleaning device is a spin cleaner. A chuck table of the spin cleaner holds the obverse surface of the wafer, and the chuck table is rotated while cleaning water is supplied to the reverse surface of the wafer to eliminate the sludge, etc. adhered to the reverse surface of the wafer.
Since microchips have been formed on the obverse surface of the wafer in a pretreatment, a protection film is attached on the obverse surface of the wafer in order to protect the microchips. The surface grinding apparatus grinds and cleans the wafer with the protection film attached thereon, and thereafter, the wafer is transferred to a protection film separation stage. For example, an adhesive tape is stuck on the protection film, and the protection film as well as the tape is peeled from the wafer.
Grinding the wafer thin decreases the strength of the wafer. In the case of the conventional suction disc that holds the wafer thereon with a plurality of suction pads, the peripheral part of the wafer easily chips or breaks during the transfer. Likewise, the wafer is damaged while the protection film is peeled from the wafer at the protection film separation stage.